| 摘要 |
PURPOSE:To improve the holding characteristics of stored charges in an EPROM by forming the edge section of a floating gate to a shape having rounding. CONSTITUTION:An activating region is isolated by field oxide films 12 in the main surface section of a silicon semiconductor substrate 11, a gate oxide film 13 is shaped, and a floating gate 14 by polysilicon is formed. When an inter- layer oxide film 15 is formed on the outside of the floating gate 14, a nitride film 16 is shaped on the directional dry-etched, the nitride film in surfaces vertical in the direction of etching is removed, and the nitride film 16 is left only on the side wall section of the floating gate 14. The exposed section of the gate oxide film 13 and the exposed section of the inter-layer oxide film 15 are etched by a hydrofluoric acid group solution. The nitride film 16 remaining on the side wall section functions as a mask on the next thermal oxidation, corners are taken away through oxidation in edge sections, and an electric-field concentration section is removed. The residual nitride film 16 is removed through nondirectional etching. Accordingly, the state in which an electric field unnecessarily concentrates can be avoided, and the holding characteristics of data are improved. |
